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Respiration

Respiratory substrates and investigating respiration in yeast

  • 3 things to know
  • Component 1

Overview

How a lipid is used as a respiratory substrate, how an amino acid is used as a respiratory substrate and respiratory quotient.

What you need to know

Answer each one before you reveal it.

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Key term

Explain why the respiratory quotient of a lipid is below 1.

Key term

Explain how a respirometer measures the rate of oxygen uptake.

Key term

Which molecule is the usual respiratory substrate of a cell?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Which molecule is the usual respiratory substrate of a cell?

    Model answer

    Glucose, which is why the pathways of respiration are described in terms of its breakdown.

  2. 2

    Describe how a lipid is used as a respiratory substrate.

    Model answer

    It is hydrolysed to glycerol and fatty acids, the glycerol is converted to triose phosphate and joins glycolysis, and the fatty acid chains are cut into two-carbon units that enter the Krebs cycle as acetyl coenzyme A.

  3. 3

    Explain why a lipid yields so much more ATP per gram than a carbohydrate.

    Model answer

    A long fatty acid chain supplies many acetyl groups and therefore many reduced coenzymes, because it carries far more hydrogen per unit mass than a sugar does.

  4. 4

    Describe how an amino acid is used as a respiratory substrate.

    Model answer

    It is deaminated in the liver and the remainder of the molecule is converted, according to which amino acid it was, into pyruvate, acetyl coenzyme A or an intermediate of the Krebs cycle.

  5. 5

    What is deamination?

    Model answer

    The removal of the amino group from an amino acid, which in a mammal is converted to ammonia and then to urea for excretion.

  6. 6

    Why is protein normally used as a respiratory substrate only as a last resort?

    Model answer

    Proteins are needed as enzymes and structural components, and their nitrogen must be excreted as urea, which itself costs energy and water.

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